The invention pertains to apparatus and methods for teaching a robot the position and orientation of drillhole centerlines, by examination of drillholes in a master part, so that the robot can perform a drill sequence in additional workpieces so as to produce production parts corresponding to the master part.
Techniques for programming a robot to carry out a drill sequence based upon numeric control information are well known, but it is time consuming and somewhat difficult even for a skilled person to develop such control information mathematically, especially when the position and orientation of the holes relative to the master part are not available in computer-readable form. Techniques also have been worked out for teaching a robot a drillhole configuration based upon manual sequencing of probing actions on a master part. During a single pass through the drill sequence under control of the human operator, the robot learns the sequence, and can thereafter duplicate the sequence. The drawback of this procedure is that it requires a skilled operator a significant period of time to go through the proper drill sequence. Under certain circumstances the operator will not be able to view the master part properly or have the dexterity in control required to locate the drillholes properly and particularly may not have the capability to provide the proper pitch and yaw coordinates to match the drillhole in the master part.
Most drillholes are drilled normal to the tangential plane of the hole or its approximation at the point of entry, which may be termed the "scribe crosspoint."
In a typical robot hole drilling application, it is important that the robot orient the drill along the desired centerline of the drillhole and move the drill along the centerline while drilling the hole. Improperly locating the drill bit will cause the hole to be drilled in the wrong place; misorientation of the drill relative to the drillhole centerline will cause the hole to be misdirected; misorientation of the drill bit relative to the surface being drilled might cause the hole to be misshapen. The drill bit must contact the surface of the workpiece at a predetermined scribe crosspoint having determinable X, Y, Z coordinates in relation to the workpiece, and the drill axis must be controlled in pitch and yaw to follow the desired centerline orientation. In most drilling operations, the depth of the drillhole is not critical.
In order to use a robot drilling system, data is necessary to determine the scribe crosspoint surface position and centerline orientation of each hole to be drilled. If this data is unavailable in a design data base, then the data must be derived through some form of teaching. Furthermore, teaching may be necessary, even when design data is available, in order to compensate for positional inaccuracies in the robot itself.
Sophisticated programmable robots are capable of using drillhole coordinates relative to the coordinate system of the workpiece to be drilled. Sensory data and calibration software are then used to locate the workpiece and to compute how to position the robot's joints so as to provide proper juxtaposition of the workpiece and the drill bit. A teaching session for such robot drilling systems involves the following steps:
(1) Set up a master part at the robot drilling station. PA0 (2) Calibrate the master part coordinate system. PA0 (3) Teach the coordinates of each drillhole relative to the master part and store these coordinates for future playback. PA0 (1) It is tedious and time consuming. PA0 (2) Its accuracy is limited, especially for determining drillhole centerline orientation. PA0 (3) It may be necessary for the person doing the teaching to place his head inside the work envelope of the robot in order to see the precise relation of the drill bit to the drillhole in the master part. This may constitute a safety hazard.
The standard method of teaching drillhole coordinates is to operate the robot as a teleoperator, positioning the drill manually at each hole to be drilled. This procedure has a number of disadvantages as follows:
Techniques in the prior art have been developed using special targets to ascertain the coordinates of the desired drillhole axis, by multiple contacts with a multiple probe under computer control, after an initial approximate orientation is made by manual control. D. M. Lambeth, "An Approach to Tactile Feedback Programming for Robotic Drilling," Robot VI Conference, Society of Manufacturing Engineers (MS82-120), Mar. 2-4, 1982.